Why do you oppose allowing states to decide their own abortion laws?

If you want to live in a state that allows abortion, you are free to reside in that state. If a woman wants an abortion, they are free to travel to that state and get an abortion. The tenth amendment gives states some degree of sovereignty:

[b]The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people. [/b]

If it's not in the constitution, which abortion isn't, it's left up to the state to decide - as long as state laws don't violate the constitution. A woman's right to protect her own life is a constitutional right. All states that have abortion laws have a provision that allows women to terminate their pregnancy in those life-threatening situations. Beyond that, there's nothing in the constitution that would give a woman the right to murder her own baby.